Cool. But I wonder about calories per acre, and if there is a way to account for necessary crop rotation and soil depletion.
IIRC, crop rotation and soil depletion has a few more variables to account for-- soil type, current nutrients, what you are/aren't willing to fertilize with.
Potatoes for example should need 220 lbs nitrogen/yr [1] and soybeans or peanuts should be able to put that back after a year [2].
1: http://www.extension.uidaho.edu/nutrient/crop_nutrient/potat... 2: http://aces.nmsu.edu/pubs/_a/A129/